A human being is formed
This is the most possible cause to thalidomide induced birth defects.
The foetus is not particularly what one call a "pretty baby”, but more something of what only a mother could love. It has become four weeks old and the menstruation of the mother is one week out of time. In the front the embryo is dominated by a blunt head-end with a big primitive mouth right above the heart. In the rear is the body elongated in a tail. Now is the time for the rudiments of arms, legs, brain, spine, face, nervous system and interior organs to form. Everywhere in the body the rudiments need an exceed of oxygen and nutrients to grow.
Vaguely see the fingers in the fifth week
Already in the next; the fifth week, one can, for example, vaguely see five fingers in the top of the arm bud. Along this top there is a growth-zone where a continues interaction between individual cells in the growth-zone and underlying cells in the "limb bud" tissue rules the evolution of the whole arm. The mechanism is analogues in other extremities or organs.
The foetus is only about one millimetre in body-length and the mother doesn't even know she is pregnant. During a few intense weeks, beginning in the fourth week, all organs and limbs are beginning to develop. Thalidomide exhibited ant angiogenesis characteristics, preventing vascularisation in the "limb bud" tissue of developing embryos.
The chemical molecule thalidomide could reach the embryo through the placenta. Physicians have showed that thalidomide is sub versed very rapidly sin the human body. 30 minutes after taking a tablet, the effects are gone. In the same way will the growth of the foetus take place during "active periods?” First if these two conditions were correlating; the embryo was affected. There are cases in literature where a twin in a pair of identical twins is completely un-affected, while the other twin shows severe thalidomide-induced birth-defects.
Thalidomide during "active periods”
The mother had to take thalidomide simultaneously with the foetus "active periods” to cause a
thalidomide embryopathy. The process of limb, or organ, growth involves the induction of cytokines
(tissue hormones that facilitates communication between cells) which stimulate new blood vessel growth (angiogenesis) into developing limb buds, or organs. Thalidomide inhibits these cytokines and blocks
angiogenesis, causing insufficient nutrient and oxygen delivery to the developing organs, or limbs.
Blood vessels acts as a "road-map”
Angiogenesis in new blood vessel growth acts as a "road-map” for the continues development of the limb, or organ. When the chemical signal to the cells in the growth-zone is inhibited they can't function normally and the interaction with under-lying tissues is disturbed. As the development of the foetus is continues according to the genetic clock, the embryo can't reverse the development and re-do a prior step that went wrong: The result is a malformation. The more frequent exposition to the drug and the higher the dose; the higher the probability for more severe disturbances of the development. Taking only one 100 mg. tablet early in pregnancy, when limb buds, and organs, are forming, could be enough to give birth-defects.